Abstract:

A photoreceptor including a layer including a crosslinked material
obtained by polymerizing at least a vinyl group-containing triarylamine
compound, a radically polymerizable monomer which has at least three
radically polymerizable groups in a molecule and has no charge transport
structure, and an optional radically polymerizable polycarbonate. An
image forming apparatus including the photoreceptor, a charger configured
to charge the photoreceptor, a light irradiating device configured to
irradiate the charged photoreceptor to form an electrostatic latent
image; a developing device configured to develop the electrostatic latent
image with a developer including a toner to form a toner image, and a
transferring device configured to transfer the toner image onto a
receiving material.

Claims:

1. A photoreceptor comprising:a layer including a crosslinked material
obtained by polymerizing at least a vinyl group-containing triarylamine
compound having the below-mentioned formula (1), and a radically
polymerizable monomer which has at least three radically polymerizable
groups in a molecule and has no charge transport structure: ##STR00029##
wherein Ar represents an aryl group or a substituted aryl group.

2. The photoreceptor according to claim 1, wherein the crosslinked
material is obtained by polymerizing at least a vinyl group-containing
triarylamine compound having formula (1), a polycarbonate having a
radically polymerizable group, and a radically polymerizable monomer
which has at least three radically polymerizable groups in a molecule and
has no charge transport structure.

3. The photoreceptor according to claim 2, wherein the polycarbonate has
the following formula (5): ##STR00030## wherein k and j represent molar
ratio of units, and each of k and j is a positive integer; and n is a
repeat number of the units and is a positive integer.

4. The photoreceptor according to claim 1, wherein the vinyl
group-containing triarylamine compound is a tristyrylstyryl amine
compound having the following formula (2): ##STR00031##

5. The photoreceptor according to claim 1, wherein the vinyl
group-containing triarylamine compound is a tristyrylstyryl amine
compound having the following formula (3): ##STR00032## wherein R1
represents an alkyl group having not greater than 8 carbon atoms, an
alkenyl group having not greater than 8 carbon atoms, an alkoxyl group
having not greater than 8 carbon atoms, an aryl group having not greater
than 8 carbon atoms, or an alaryl group having not greater than 8 carbon
atoms; and n is 0, 1, 2 or 3.

6. The photoreceptor according to claim 1, wherein the radically
polymerizable monomer which has at least three radically polymerizable
groups in a molecule and has no charge transport structure is
1,2,4-trivinylcyclohexane having the following formula (4): ##STR00033##

7. The photoreceptor according to claim 6, wherein the crosslinked
material is obtained by polymerizing at least a vinyl group-containing
triarylamine compound having the below-mentioned formula (2), and the
radically polymerizable monomer having formula (4) without using a
polymerization initiator: ##STR00034##

8. The photoreceptor according to claim 6, wherein the crosslinked
material is obtained by polymerizing at least a vinyl group-containing
triarylamine compound having the below-mentioned formula (2), a
polycarbonate having a radically polymerizable group, and the radically
polymerizable monomer having formula (4) without using a polymerization
initiator: ##STR00035##

9. The photoreceptor according to claim 1, wherein the radically
polymerizable monomer is a radically polymerizable monomer which has
three radically polymerizable groups in a molecule and has no charge
transport structure or a combination of a radically polymerizable monomer
which has three radically polymerizable groups in a molecule and has no
charge transport structure and a radically polymerizable monomer which
has five or six radically polymerizable groups in a molecule and has no
charge transport structure.

10. The photoreceptor according to claim 1, wherein the layer is an
outermost layer of the photoreceptor.

11. The photoreceptor according to claim 1, further comprising:a
substrate;a charge generation layer configured to generate a charge,
which is located overlying the substrate; anda charge transport layer
configured to transport the charge, which is located on the charge
generation layer,wherein the layer including the crosslinked material is
located overlying the charge transport layer as an outermost layer.

12. The photoreceptor according to claim 11, wherein the crosslinked
material is obtained by polymerizing at least a vinyl group-containing
triarylamine compound having formula (1), a polycarbonate having a
radically polymerizable group, and a radically polymerizable monomer
which has at least three radically polymerizable groups in a molecule and
has no charge transport structure.

13. An image forming method comprising:charging the photoreceptor
according to claim 1;irradiating the charged photoreceptor with imagewise
light to form an electrostatic latent image on the
photoreceptor;developing the electrostatic latent image with a developer
including a toner to form a toner image on the photoreceptor;
andtransferring the toner image onto a receiving material.

14. The image forming method according to claim 13, wherein the imagewise
light is light modulated by digital image signals.

15. An image forming apparatus comprising:the photoreceptor according to
claim 1;a charger configured to charge the photoreceptor;a light
irradiating device configured to irradiate the charged photoreceptor with
imagewise light to form an electrostatic latent image on the
photoreceptor;a developing device configured to develop the electrostatic
latent image with a developer including a toner to form a toner image on
the photoreceptor; anda transferring device configured to transfer the
toner image onto a receiving material.

16. The image forming apparatus according to claim 15, wherein the light
irradiating device irradiates the charged photoreceptor with light
modulated by digital image signals to form an electrostatic latent image
on the photoreceptor.

17. A process cartridge comprising:the photoreceptor according to claim 1;
andat least one of a charger configured to charge the photoreceptor;a
light irradiating device configured to irradiate the charged
photoreceptor with imagewise light to form an electrostatic latent image
on the photoreceptor;a developing device configured to develop the
electrostatic latent image with a developer including a toner to form a
toner image on the photoreceptor;a transferring device configured to
transfer the toner image onto a receiving material; anda cleaner
configured to clean a surface of the photoreceptor after then toner image
is transferred onto the receiving material,wherein the process cartridge
is detachably attachable to an image forming apparatus as a unit.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to an electrophotographic
photoreceptor. In addition, the present invention also relates to an
image forming method, an image forming apparatus, and a process cartridge
using the electrophotographic photoreceptor.

[0003]2. Discussion of the Related Art

[0004]Organic photoreceptors have various advantages over inorganic
photoreceptors because of having good properties. Therefore, organic
photoreceptors have been typically used for image forming apparatus such
as copiers, facsimiles, laser printers and multifunctional products
having copying, facsimileing and printing functions. The advantages
thereof are as follows:

(1) Wide optical absorption wavelength range and large light absorption
amount (i.e., good optical properties);(2) High photosensitivity and good
charging property (i.e., good electric properties);(3) Wide flexibility
in selecting materials therefor (i.e., various materials can be used
therefor);(4) Good productivity (i.e., they can be easily
manufactured);(5) Low manufacturing costs; and(6) Good safeness (i.e.,
they are nontoxic).

[0005]Recently, a need exists for a miniaturized image forming apparatus.
Therefore, the diameter of the photoreceptors used for image forming
apparatus becomes smaller and smaller. In addition, since a need exists
for high speed and maintenance-free image forming apparatus,
photoreceptors having good durability are greatly desired. Organic
photoreceptors do not have good durability. Specifically, organic
photoreceptors are generally soft because of typically having a charge
transport layer including a low molecular weight charge transport
material and an inactive polymer as main components. When such organic
photoreceptors are repeatedly used for electrophotographic image forming
processes (such as charging, light irradiating, developing, image
transferring and cleaning), the surfaces of the photoreceptors are easily
abraded particularly in the developing process and cleaning process.

[0006]On the other hand, in order to produce high quality images, the
particle diameter of toner used as a developer in image forming apparatus
becomes smaller and smaller. In order to well remove such small toner
from the surface of a photoreceptor using a cleaning blade, the hardness
of the blade has to be increased, and in addition the pressure of the
blade contacted with the photoreceptor has to be increased, thereby
accelerating abrasion of the surface of the photoreceptor. When the
surface of a photoreceptor is abraded, the electric properties (such as
photosensitivity and charging property) of the photoreceptor deteriorate,
resulting in formation of abnormal images (such as low density images and
images with background fouling). When a portion of a photoreceptor is
mainly abraded, an abnormal streak image is formed.

[0007]In attempting to solve the abrasion problem, various proposals have
been made. For example, a published unexamined Japanese patent
application No (herein after referred to as JP-A) 56-48637 discloses a
charge transport layer including a crosslinked binder resin. JP-A 64-1728
(corresponding to U.S. Pat. No. 4,956,440) discloses a charge transport
polymer. JP-A 04-281461 discloses a charge transport layer in which an
inorganic filler is dispersed. JP-A 08-262779 discloses a photoreceptor
in which a crosslinked acrylic resin is included in the outermost layer.
JP-As 05-216249 (corresponding to U.S. Pat. Nos. 5,411,827 and 5,496,671)
and 05-323630 have disclosed charge transport layers which are prepared
by heating or light-irradiating a monomer having a C--C double bond, a
charge transport material having a C--C double bond, and a binder resin
to react the monomer with the charge transport material. JP-A 2000-66425
(corresponding to U.S. Pat. No. 6,180,303) and 2000-206717 (corresponding
to U.S. Pat. No. 6,416,915) have disclosed photosensitive layers
including a material obtained by crosslinking a hole transport material
having at least two chain-polymerizable functional groups in a molecule.

[0008]By using these techniques, the abrasion resistance of organic
photoreceptors is improved. However, these photoreceptors tend to cause a
new problem. Specifically, when foreign materials are adhered to or a
scratch is made on the surfaces of conventional photoreceptors having
relatively low abrasion resistance, the foreign materials are easily
removed therefrom or the scratch disappears due to refacing of the
photoreceptors. Therefore, abnormal images caused by the foreign
materials or the scratch are formed only for a short time. In contrast,
in the case of the above-mentioned photoreceptors having good abrasion
resistance, abnormal images are formed for a relatively long time because
the surfaces thereof are hardly refaced and foreign materials are not
easily removed therefrom or the scratch hardly disappears.

[0009]In particular, recent image forming apparatus are required to
produce high quality images while saving energy. Therefore, such image
forming apparatus typically use toner having a small particle diameter
and a low softening point, and including a particulate inorganic material
(such as silica) as an additive (fluidizer). Such image forming apparatus
tend to cause a problem in that a particulate inorganic material (silica)
sticks into the surface of the photoreceptor thereof in the developing
process, and a wax component included in the toner accumulates around the
stuck inorganic material, resulting in formation of a white spot in a
solid image.

[0010]Because of these reasons, a need exists for a photoreceptor which
has good abrasion resistance and can produce high quality images over a
long period of time without producing defective images such as white spot
images.

SUMMARY OF THE INVENTION

[0011]As an aspect of the present invention, a photoreceptor is provided,
which includes a layer including a crosslinked material obtained by
polymerizing at least a vinyl group-containing triarylamine compound
having the below-mentioned formula (1), and a radically polymerizable
monomer which has at least three radically polymerizable groups in a
molecule and has a non-triarylamine structure (i.e., no charge transport
structure):

##STR00001##

wherein Ar represents an aryl group or a substituted aryl group.

[0012]The crosslinked material may be obtained by polymerizing at least a
vinyl group-containing triarylamine compound having formula (1), a
polycarbonate having a radically polymerizable group, and a radically
polymerizable monomer which has at least three radically polymerizable
groups in a molecule and has a non-triarylamine structure (i.e., no
charge transport structure).

[0013]Another aspect of the present invention, an image forming method is
provided, which includes:

[0014]charging the photoreceptor mentioned above;

[0015]irradiating the charged photoreceptor with light to form an
electrostatic latent image thereon;

[0016]developing the electrostatic latent image with a developer including
a toner to form a toner image on the photoreceptor; and

[0017]transferring the toner image onto a receiving material.

[0018]Yet another aspect of the present invention, an image forming
apparatus is provided, which includes:

[0019]the photoreceptor mentioned above;

[0020]a charger configured to charge the photoreceptor;

[0021]a light irradiating device configured to irradiate the charged
photoreceptor with imagewise light to form an electrostatic latent image
thereon;

[0022]a developing device configured to develop the electrostatic latent
image with a developer including a toner to form a toner image on the
photoreceptor; and

[0024]As a further aspect of the present invention, a process cartridge is
provided, which includes:

[0025]the photoreceptor mentioned above;

[0026]at least one of a charger, a light irradiating device, a developing
device, a transferring device, a cleaner configured to clean a surface of
the photoreceptor, and a discharger configured to reduce charges
remaining on the photoreceptor.

[0027]These and other objects, features and advantages of the present
invention will become apparent upon consideration of the following
description of the preferred embodiments of the present invention taken
in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic diagram illustrating an example of the image
forming apparatus of the present invention and for explaining the image
forming method of the present invention;

[0029]FIG. 2 is a schematic diagram illustrating another example of the
image forming apparatus of the present invention;

[0030]FIG. 3 is a schematic diagram illustrating an example of the process
cartridge of the present invention; and

[0032]At first, the photoreceptor of the present invention will be
explained.

[0033]The photoreceptor of the present invention has a layer including a
crosslinked material obtained by polymerizing at least a vinyl
group-containing triarylamine compound having the below-mentioned formula
(1), and a radically polymerizable monomer which has at least three
radically polymerizable groups in a molecule and has a non-triarylamine
structure (hereinafter referred to as no charge transport structure):

##STR00002##

wherein Ar represents an aryl group or a substituted aryl group.

[0034]The crosslinked material may be obtained by polymerizing at least a
vinyl group-containing triarylamine compound having formula (1), a
polycarbonate having a radically polymerizable group, and a radically
polymerizable monomer which has at least three radically polymerizable
groups in a molecule and has no charge transport structure.

[0035]The polymerization reaction can be typically performed by heating
the above-mentioned compounds.

[0036]It is well known to perform crosslinking polymerization by
subjecting a radically polymerizable material to a radiation (such as UV
and EB) irradiation treatment or a heat treatment (or without performing
such a treatment) in the presence or absence of a polymerization
catalyst. In addition, it is well known that such crosslinkable materials
cause volume decrease when crosslinked, and particularly UV crosslinkable
materials cause serious volume decrease. In this regard, the crosslinked
materials are distorted due to internal stress caused by the volume
decrease, resulting in deterioration of the mechanical strength of the
crosslinked materials.

[0037]In the present invention, the radical polymerization reaction is
also caused in a drying process in which the coated radical polymerizable
compounds are heated to be dried. It is considered that the heat applied
to the compounds in the drying process not only proceeds the crosslinking
reaction but also relaxes the internal stress, but the detailed
crosslinking mechanism is not yet determined. However, the present
inventors discover that a crosslinked layer (film) cannot be prepared by
radical polymerization if a compound (I) (i.e., a compound having a
structure such that a vinyl group is connected with a triphenylamine
group via a conjugated bond group) is not used.

[0038]The photoreceptor of the present invention has a good combination of
abrasion resistance and electric property. In addition, an external
additive (such as silica) included in toner used for the developer and
having a high hardness hardly sticks into the surface of the
photoreceptor, and therefore the above-mentioned white spot problem is
hardly caused. The reason therefor is considered as follows.

[0039]The outermost layers of conventional photoreceptors are typically
constituted of a thermoplastic resin in which a low molecular weight
charge transport material is dispersed and which is relatively soft
compared to inorganic fillers such as silica included in toner.
Therefore, when such conventional photoreceptors are contacted with the
toner, the inorganic fillers easily stick into the outermost layers of
the photoreceptors. Therefore, it is necessary to enhance the hardness of
the outermost layers to prevent occurrence of the problem. The hardness
of the outermost layers is hardly enhanced by replacing the low molecular
weight with a charge transport polymer, and it is necessary to use a
crosslinked resin having a high crosslinking density for the outermost
layers. In particular, a crosslinked layer prepared by using a
multifunctional monomer is preferably used as an outermost layer.

[0040]On the other hand, in order to impart good electric properties to a
photoreceptor, a charge transport component is preferably included in the
crosslinked outermost layer. In general, components having a triarylamine
structure are typically used as charge transport components. Triarylamine
has a pyramid-like structure (i.e., a bulky structure) such that three
aryl groups are connected with a nitrogen atom, which is present at the
peak of the pyramid, wherein the bond angle formed by any two aryl groups
is 108°. In addition, monomers having a triarylamine structure
have a relatively large molecular weight. Therefore, by using such a
triarylamine monomer, the resultant crosslinked layer cannot have a high
crosslinking density.

[0041]Among various groups having a triarylamine structure, the minimum
unit is the triphenylamine group. In the case where a polymerizable group
is directly connected with the triphenylamine group, the molecular motion
of the crosslinked material is restricted, resulting in deterioration of
the charge mobility of the resultant layer. Therefore, the resultant
photoreceptor has poor electric properties. Accordingly, it is preferable
that the charge transport material has a relatively long conjugated
system. However, in this case the crosslinking density decreases. The
crosslinking density is an important factor, and by increasing the
crosslinking density, the mechanical hardness and electrostatic
properties of the resultant layer can be enhanced. However, a layer
having as high mechanical hardness as possible is not necessarily
preferable as the outermost layer of a photoreceptor, which is repeatedly
rubbed by other members (such as developers and cleaning blades), and the
layer preferably has toughness as well as hardness. It is considered to
be preferable to use a layer having good combination of hardness and
toughness as the outermost layer.

[0042]When the cross linked material is prepared by polymerizing a monomer
having a high polarity (such as acrylic monomers), the resultant
crosslinked material has a high specific dielectric constant. In this
case, the charge transportability of the layer deteriorates. In contrast,
in the present invention, the compound having a charge transportability
has a vinyl group, which has low polarity, and therefore the resultant
layer has good charge transportability while the layer is well
crosslinked by radical polymerization.

[0043]Thus, in order to fulfill all of the requirements mentioned above,
at least a triarylamine compound having a vinyl group, which serves as a
charge transport component, and a radically polymerizable vinyl monomer
having no charge transport structure are used for the photoreceptor of
the present invention. In addition, a polycarbonate having a radically
polymerizable group can be used in combination with a triarylamine
compound having a vinyl group, and a radically polymerizable vinyl
monomer having no charge transport structure.

[0044]Suitable compounds for use as the radically polymerizable monomer
having no charge transport structure include radically polymerizable
vinyl monomers having a non-pyramid structure.

[0045]Specific examples of such radically polymerizable vinyl monomers
include (i) comb polymers having at least three vinyl groups in the side
chains and/or main chain and having the below-mentioned formula (1); (ii)
cyclic monomers having cyclic carbon atoms with which at least three
vinyl groups are connected and having the below-mentioned formula (ii);
(iii) monomers having a methane-form structure (i.e., monomers having a
non-pyramid structure such that a carbon atom is present at the peak of
the structure, and four groups extending in the four directions are
connected with the center carbon atom (for example, one of the four
groups is a hydrogen atom, and the residual three groups are vinyl
groups).

##STR00003##

wherein each of R3 to R8 represents a hydrogen atom, a
substituted or unsubstituted hydrocarbon group, which may be branched, or
a hydroxyl group; each of R1 and R2 represents a radical
polymerizable group; each of X1 to X3 represents a divalent
organic group; n is a positive integer; and each of j, k and m is 0 or 1

##STR00004##

wherein each of R9 to R12 represents a carbon atom, wherein
R9 to R12 constitute a carbon ring; each of R13 to
R16 represents a hydrogen atom, a substituted or unsubstituted
hydrocarbon group, which may be branched, a hydroxyl group, or a
radically polymerizable group, wherein each of at least three of R13
to R16 is a radically polymerizable group; each of X4 to
X7 represents a divalent organic group; each of p and q is 0 or a
positive integer, wherein p+q≧1; and each of r, s, t and u is 0 or
1.

[0046]In this regard, for example, when p is 0, the compound has a
three-membered ring without a group including X5 and R14.

##STR00005##

wherein each of R17 to R19 is a radically polymerizable group;
each of X8 to X10 represents a divalent organic group; and each
of v, w and y is 0 or 1.

[0047]Thus, a layer having good electric properties and an extremely high
crosslinking density can be prepared. Therefore, the photoreceptor of the
present invention fulfills the photoreceptor requirements mentioned above
while hardly causing the sticking problem in that inorganic fillers stick
into the surface of the photoreceptor, resulting in prevention of
formation of white spot images.

[0048]In this regard, the crosslinked material mentioned above preferably
has a gel fraction of not less than 95%, and more preferably not less
than 97% so that the resultant photoreceptor has excellent abrasion
resistance and can produce images with few image defects over a long
period of time. In addition, the radically polymerizable monomer having
no charge transport structure has at least three radically polymerizable
groups in a molecule to impart a good combination of abrasion resistance
and scratch resistance to the resultant layer, and it is preferable to
use a radically polymerizable monomer having at least five or six
radically polymerizable groups in a molecule to enhance the properties.

[0049]By using the above-mentioned photoreceptor of the present invention,
an image forming method, an image forming apparatus, and a process
cartridge, which can produce high quality images over a long period of
time, can be provided.

[0050]Next, the photoreceptor of the present invention will be explained
in detail.

[0051]The photoreceptor of the present invention has a layer including a
crosslinked material obtained by radically polymerizing at least a
vinyl-group containing triarylamine compound serving as a charge
transport component and having formula (1), and a radically polymerizable
monomer compound having no charge transport structure, for example,
without using a polymerization initiator, and optionally has another
layer. In this regard, the crosslinked material may be prepared by
radically polymerizing at least a vinyl-group containing triarylamine
compound serving as a charge transport component and having formula (1),
a polycarbonate having a radically polymerizable group, and a radically
polymerizable monomer compound having no charge transport structure, for
example, without using a polymerization initiator.

[0052]Next, the layer including a crosslinked material will be explained
in detail.

[0053]The layer includes at least a crosslinked material, which is
prepared by radically polymerizing at least a vinyl-group containing
triarylamine compound serving as a charge transport component and having
the below-mentioned formula (1), and a radically polymerizable monomer
compound having no charge transport structure.

##STR00006##

[0054]In this regard, the crosslinked material may be prepared by
radically polymerizing at least a vinyl-group containing triarylamine
compound serving as a charge transport component and having formula (1),
a polycarbonate having a radically polymerizable group, and a radically
polymerizable monomer compound having no charge transport structure. The
layer optionally includes another component, if necessary. wherein Ar
represents an aryl group or a substituted aryl group.

[0055]Specific examples of such an aryl group include stilbenzyl and
biphenyl groups. Stilbenzyl groups are connected with the nitrogen atom
and the vinyl group in the cis-form or trans-form. Biphenyl groups are
connected with the nitrogen atom at the para-position or meta-position
thereof. Vinyl groups are connected with the stilbenzyl group or biphenyl
group at the para-position or meta-position thereof.)

[0056]It is preferable that in formula (1) all of the three aryl groups Ar
are the same as each other. It is also preferable that one of the three
aryl groups has a substituent and therefore the compound has an
imbalanced structure. Specifically, vinyl group-containing triarylamine
compounds having the following formula (3) are preferably used.

##STR00007##

wherein R1 represents an alkyl group having not greater than 8 carbon
atoms, an alkenyl group having not greater than 8 carbon atoms, an
alkoxyl group having not greater than 8 carbon atoms, an aryl group
having not greater than 8 carbon atoms, or an alaryl group having not
greater than 8 carbon atoms; and n is 0, 1, 2 or 3.

[0057]In addition, among vinyl group-containing triarylamine compounds
having formula (1), tristyrylstyrylamine compounds having the following
formula (2) are preferably used.

##STR00008##

[0058]Specific examples of the aryl group Ar of the vinyl group-containing
triarylamine compounds having formula (1) are shown in Table 1 below, but
are not limited thereto.

[0059]Next, the method for preparing vinyl group-containing triarylamine
compounds having formula (1) will be explained.

[0060]For example, an aldehyde compound is synthesized, and then the
aldehyde compound is reacted with a phosphonium salt compound to prepare
a vinyl group-containing triarylamine compound. Alternatively, a bromo
compound is reacted with a boronic acid compound to prepare a vinyl
group-containing triarylamine compound.

[0061]The method will be explained in detail.

<Example 1 of Synthesis of Aldehyde Compound>

[0062]As illustrated in the below-mentioned reaction formula, a
tribromotriphenylamine compound is formylated using a conventional method
to prepare an aldehyde compound.

##STR00015##

[0063]Suitable methods for preparing the intermediate compounds (i.e.,
aldehyde compounds) using the above-mentioned reaction include methods
using lithium/dimethylformamide, but are not limited thereto. Specific
examples of the methods are explained in Examples below.

<Example 2 of synthesis of aldehyde compound>

[0064]As illustrated in the below-mentioned reaction formula, a
triphenylamine compound is formylated using a conventional method to
prepare an aldehyde compound.

##STR00016##

[0065]Suitable methods for preparing the intermediate compounds (i.e.,
aldehyde compounds) using the above-mentioned reaction include methods
using zinc chloride/phosphorous oxychloride/dimethylformamide, but are
not limited thereto. Specific examples of the methods are explained in
Examples below.

[0066]As illustrated in the below-mentioned reaction formula, an aldehyde
compound is reacted with a phosphonium salt compound using a conventional
synthesis method to prepare a vinyl group-containing triarylamine
compound.

##STR00017##

[0067]Suitable methods for preparing the vinyl group-containing
triarylamine compounds using the above-mentioned reaction include the
Wittig method using potassium t-butoxide/dimethylfromamide, but are not
limited thereto. Specific examples of the methods are explained in
Examples below.

[0068]As illustrated in the below-mentioned reaction formula, a bromo
compound is reacted with a boronic acid compound using a conventional
synthesis method to prepare a vinyl group-containing triarylamine
compound.

##STR00018##

[0069]Suitable methods for preparing the vinyl group-containing
triarylamine compounds using the above-mentioned reaction include the
Suzuki Coupling Reaction method using potassium carbonate/triphenyl
phosphine palladium catalyst, but are not limited thereto. Specific
examples of the methods are explained in Examples below.

[0070]As mentioned above, the vinyl group-containing triarylamine
compounds for use in preparing the photoreceptor of the present invention
have a triarylamine structure such that a stilbenzyl group or a biphenyl
group is included in the structure, i.e., an extended conjugated system
is included therein. Therefore, the vinyl group-containing triarylamine
compounds have high hole mobility (i.e., good charge transportability).
In addition, since a vinyl group is incorporated in the triarylamine
compounds, the compounds have good chain polymerizability (for example,
good radical polymerizability)

[0071]Therefore, even when a polymerization initiator is not used, a
crosslinked layer having a high crosslinking density can be prepared by
radically polymerizing the compounds. Alternatively, a crosslinked layer
having a high crosslinking density can be prepared by irradiating the
compounds with ultraviolet rays (UV), electron beams (ER), and radiation
ray or by using a radical polymerization initiator. The resultant
crosslinked layer has a good combination of film forming property,
mechanical resistance (e.g., abrasion resistance), heat resistance, and
charge transportability. Therefore, the layer (film) can be preferably
used as an organic functional material for use in organic photoreceptors,
organic electroluminescence devices (EL), organic thin film transistors
(TFT), and organic semiconductors such as solar batteries.

[0073]One or more of these monomers can be used in combination with the
vinyl group-containing trimethylamine compounds so that the resultant
layer has the desired properties. The added amount of these monomers is
0.01 to 1,500 parts by weight, and preferably from 1 to 500 parts by
weight, based on 100 parts by weight of the vinyl group-containing
trimethylamine compounds used.

[0074]As mentioned above, when preparing the crosslinked material, a
radically polymerizable monomer having at least three radically
polymerizable groups and having no charge transport structure is used in
combination with a vinyl group-containing triarylamine compound.
Specifically, the monomers have at least three radically polymerizable
groups and do not include hole transport structures such as triarylamine
structure, hydrazone structure, pyrazoline structure, and carbazole
structure; and electron transport structures (or electron transport
groups) such as condensed polycyclic quinone structure, diphenoquinone
structure, and electron accepting aromatic groups including a cyano or
nitro group.

[0075]Suitable radically polymerizable functional groups included in the
monomers include groups, which have a C--C double bond and are radically
polymerizable. Specific examples of the radically polymerizable
functional groups include 1-substituted ethylene groups and
1,1-substituted ethylene groups, which are explained below.

(1-Substituted Ethylene Groups)

[0076]Specific examples of the 1-substituted ethylene groups include the
following group (6):

CH2═CH--X1-- (6)

wherein X1 represents a substituted or unsubstituted arylene group
(such as phenylene and naphthylene groups), a substituted or
unsubstituted alkenylene group, a --CO-- group, a --COO-- group, a
--CON(R1) group (R1 represents a hydrogen atom, an alkyl group
(e.g., methyl and ethyl groups), an aralkyl group (e.g., benzyl,
naphthylmethyl and phenetyl groups), or an aryl group (e.g., phenyl and
naphthyl groups)) or a --S-- group.

[0077]Specific examples of the groups having formula (6) include a vinyl
group, a styryl group, 2-methyl-1,3-butadienyl group, a vinylcarbonyl
group, an acryloyloxy group, an acryloylamide group, a vinylthioether
group, etc.

(1,1-Substituted Ethylene Groups)

[0078]Specific examples of the 1,1-substituted ethylene groups include the
following group (7):

CH2═C(Y)--(X2)n-- (7)

wherein Y represents a substituted or unsubstituted alkyl group, a
substituted or unsubstituted aralkyl group, a substituted or
unsubstituted aryl group (such as phenyl and naphthyl groups), a halogen
atom, a cyano group, a nitro group, an alkoxyl group (such as methoxy and
ethoxy groups), or a --COOR2 group (wherein R2 represents a
hydrogen atom, a substituted or unsubstituted alkyl group (such as methyl
and ethyl groups), a substituted or unsubstituted aralkyl group (such as
benzyl and phenethyl groups), a substituted or unsubstituted aryl group
(such as phenyl and naphthyl groups) or a --CONR3R4 group
(wherein each of R3 and R4 represents a hydrogen atom, a
substituted or unsubstituted alkyl group (such as methyl and ethyl
groups), a substituted or unsubstituted aralkyl group (such as benzyl,
naphthylmethyl and phenethyl groups), a substituted or unsubstituted aryl
group (such as phenyl and naphthyl groups)); X2 represents a group
selected from the groups mentioned above for use in X1 and an
alkylene group, wherein at least one of Y and X2 is an oxycarbonyl
group, a cyano group, an alkenylene group or an aromatic ring group; and
n is 0 or 1.

[0079]Specific examples of the groups having formula (7) include an
α-chloroacryloyloxy group, a methacryloyloxy group, an
α-cyanoethylene group, an α-cyanoacryloyloxy group, an
α-cyanophenylene group, a methacryloylamino group, etc.

[0081]Among these functional groups, acryloyloxy and methacryloyloxy
groups are preferable. Compounds having three or more (meth) acryloyloxy
groups can be prepared by subjecting (meth)acrylic acid (salts),
(meth)acrylhalides and (meth)acrylates, which have three or more hydroxyl
groups, to an esterification reaction or an ester exchange reaction. The
radically polymerizable functional groups included in a radically
polymerizable monomer may be the same as or different from the others
therein.

[0083]Among radically polymerizable tri- or more-functional monomers
having no charge transport structure, 1,2,4-trivinylcyclohexane having
the following formula (4) is preferably used.

##STR00019##

[0084]When 1,2,4-trivinylcyclohexane is reacted with a vinyl
group-containing triarylamine compound (optionally together with a
radically polymerizable polycarbonate), it is possible to use no
polymerization initiator.

[0085]In order to form a dense crosslinked network in the crosslinked
layer, the ratio (Mw/F) of the weight average molecular weight (Mw) of a
radically polymerizable monomer having at least three functional groups
and no charge transport structure to the number of functional groups (F)
included in a molecule of the compound is preferably not greater than
250. When the number is too large, the resultant layer becomes soft and
thereby the abrasion resistance of the layer is slightly deteriorated. In
this case, it is not preferable to use only one monomer including a
functional group having an extremely long chain group when the monomer is
modified with a group such as ethylene oxide, propylene oxide and
caprolactone.

[0086]The content of the unit obtained from a radically polymerizable
monomer having at least three functional groups and no charge transport
structure in the crosslinked layer is preferably from 20 to 80% by
weight, and more preferably from 30 to 70% by weight, based on the total
weight of the crosslinked layer. The content of the unit substantially
depends on the ratio of the radically polymerizable monomer to the total
of the solid components included in the coating liquid. When the content
is too low, the three dimensional crosslinking density is low, and
thereby abrasion resistance much better than those of conventional
protective layers prepared by using a thermoplastic binder resin cannot
be imparted to the resultant layer. In contrast, when the content of the
unit is too high, the content of the charge transport compound decreases,
thereby deteriorating the electric properties of the layer. Therefore, it
is preferable that the content of the unit falls in the above-mentioned
range.

[0087]When the content of the unit in the crosslinked layer is too high,
the charge transportability of the resultant layer deteriorates,
resulting in deterioration of the photosensitivity of the photoreceptor
(i.e., increase of irradiated portions of the photoreceptor).
Particularly, when the layer including the crosslinked material has a
thickness of not less than 3 μm, there is a case where the
photoreceptor cannot function as a photoreceptor. In contrast, when the
content is too low, the crosslinking density of the resultant layer
decreases, and thereby excellent abrasion resistance cannot be acquired.

[0088]As mentioned above, a radically polymerizable polycarbonate is
optionally used in combination with a vinyl group-containing triarylamine
compound and a radically polymerizable tri- or more-functional monomer
having no charge transport structure. Among various radically
polymerizable polycarbonates, polycarbonates having the following formula
(5) are preferably used.

##STR00020##

wherein k and j represent the molar ratio of the units and each of k and j
is a positive integer; and n is the repeat number of the combined unit,
and is a positive integer.

[0089]As mentioned above, the crosslinked layer is preferably prepared by
reacting (crosslinking) at least a radically polymerizable tri- or
more-functional monomer having no charge transport structure, and a vinyl
group-containing triarylamine compound having formula (1) optionally
together with a polycarbonate having a radically polymerizable group and
a polymerization initiator. However, in order to reduce the viscosity of
the coating liquid, to relax the stress of the crosslinked layer, and to
reduce the surface energy and friction coefficient of the resultant
layer, known radically polymerizable mono- or di-functional monomers,
functional monomers and radically polymerizable oligomers can be used in
combination therewith.

[0092]Specific examples of the functional monomers include
fluorine-containing monomers such as octafluoropentyl acrylate,
2-perfluorooctylethyl acrylate, 2-perfluorooctylethyl methacrylate, and
2-perfluoroisononylethyl acrylate; vinyl monomers having apolysiloxane
group such as siloxane units having a repeat number of from 20 to 70,
which are described in JP-Ss 05-60503 and 06-45770 (e.g.,
acryloylpolydimethylsiloxaneethyl, methacryloylpolydimethylsiloxaneethyl,
acryloylpolydimethylsiloxanepropyl, acryloylpolydimethylsiloxanebutyl,
and diacryloylpolydimethylsiloxanediethyl); acrylates; and methacrylates.

[0094]When a large amount of the radically polymerizable mono- or
di-functional monomers or radically polymerizable oligomers are used, the
three dimensional crosslinking density of the crosslinked layer
decreases, thereby deteriorating the properties (such as abrasion
resistance) of the layer. Therefore, the added amount of a radically
polymerizable mono- or di-functional monomer or a radically polymerizable
oligomer is preferably not greater than 50 parts by weight, and more
preferably not greater than 30 parts by weight, per 100 parts by weight
of the radically polymerizable tri- or more-functional monomer having no
charge transport structure used.

[0095]Next, the method for synthesizing radically polymerizable tri- or
more-functional monomers having no charge transport structure will be
explained.

<Synthesis of Phosphonium Compound>

[0096]As illustrated in the below-mentioned reaction formula, a
phosphonium salt compound is synthesized from a halogenated compound
using a conventional synthesis method.

##STR00021##

[0097]Thus, the synthesis method using triphenyl phosphine is typically
used. However, the method of preparing a phosphonium salt compound
(serving as an intermediate of a radically polymerizable tri- or
more-functional monomer) is not limited thereto.

[0098]Next, the detailed synthesis method will be explained.

Synthesis Examples

Synthesis Example 1

Preparation of 4,4',4''-triformyltriphenylamine

[0099]The following components were fed into a reaction vessel equipped
with an agitator, a thermometer, and a dropping funnel.

[0101]After 65 ml of a 2.77M hexane solution of n-butyl lithium was
dropped therein, the mixture was reacted for 1 hour. In addition, after
16.45 g of dehydrated dimethylformamide was dropped therein, the mixture
was further reacted for 2 hour. The reaction product was fed into ice
water, followed by an extraction treatment using methylene chloride.
After the extracted organic phase was washed with water, the organic
phase was obtained by separation. After the organic phase was dried using
magnesium sulfate, the organic phase was condensed at a reduced pressure.
The residual material was refined using a silica gel chromatography
(solvent: toluene/ethyl acetate=9/1). Thus, 17.17 g of a yellow powder
(i.e., the target compound) was obtained. The IR spectrum of the compound
is illustrated in FIG. 4.

Synthesis Example 2

Preparation of Phosphonium Salt Compound

[0102]The following components were fed into a reaction vessel equipped
with an agitator, and a thermometer.

[0103]The components were reacted at 80° C. for 3 hours. After the
reaction, the reaction product was filtered, followed by washing using
toluene, and drying at a reduced pressure. Thus, 376 g of a white powder
(a phosphonium salt compound) was prepared. The IR spectrum of the
phosphonium salt compound is illustrated in FIG. 5.

Synthesis Example 3

Preparation of compound No. 1 listed in Table 1

[0104]The following components were fed into a reaction vessel equipped
with an agitator, and a thermometer.

[0105]The mixture was agitated while cooled by an ice bath. After 8.08 g
of potassium t-butoxide was added thereto, the mixture was reacted for 3
hours at room temperature. After the reaction, the reaction product was
fed into ice water, followed by an extraction treatment using methylene
chloride. After the extracted organic phase was washed with water, the
organic phase was obtained by separation. After the organic phase was
dried using magnesium sulfate, the organic phase was condensed at a
reduced pressure. The residual material was refined using a silica gel
chromatography (solvent: dichloromethane/cyclohexane=3/7). Thus, 9.88 g
of a yellow amorphous material (i.e., the target compound) was obtained.
The IR spectrum of the compound is illustrated in FIG. 6.

Synthesis Example 4

Preparation of compound No. 3 listed in Table 1

[0106]The following components were fed into a reaction vessel equipped
with an agitator, a thermometer, and a condenser.

[0107]The components were agitated at room temperature in an argon
atmosphere. Next, 0.3 g of tetrakistriphenylphosphine palladium (from
Tokyo Kasei Kogyo Co., Ltd.) was added to the mixture, and the mixture
was reacted for 5 hours at 70° C. After the reaction, the reaction
product was fed into ice water, followed by an extraction treatment using
methylene chloride. After the extracted organic phase was washed with
water, the organic phase was obtained by separation. After the organic
phase was dried using magnesium sulfate, the organic phase was condensed
at a reduced pressure. The residual material was refined using a silica
gel chromatography (solvent: dichloromethane/cyclohexane=1/1). Thus, 2.15
g of a pale-yellowish white powder (i.e., the target compound) was
obtained. The IR spectrum of the compound is illustrated in FIG. 7.

Synthesis Example 5

Synthesis of Tris(3-Bromophenyl)Amine (Serving as Intermediate)

[0108]The following components were fed into a reaction vessel equipped
with an agitator, a thermometer, and a condenser.

[0109]The mixture was agitated for 24 hours while refluxed in an argon
atmosphere to be reacted. After the reaction, the reaction product was
fed into ice water, followed by an extraction treatment using methylene
chloride. After the extracted organic phase was washed with water, the
organic phase was obtained by separation. After the organic phase was
dried using magnesium sulfate, the organic phase was condensed at a
reduced pressure. The residual material was refined using a silica gel
chromatography (solvent: dichloromethane/cyclohexane=1/5), followed by a
recrystallization refinement treatment using ethanol. Thus, 7.02 g of a
white powder (i.e., the target compound) was obtained. The IR spectrum of
the compound is illustrated in FIG. 8.

[0111]The components were agitated at room temperature in an argon
atmosphere. Next, 0.35 g of tetrakistriphenylphosphine palladium (from
Tokyo Kasei Kogyo Co., Ltd.) was added to the mixture, and the mixture
was reacted for 5 hours at 70° C. After the reaction, the reaction
product was fed into ice water, followed by an extraction treatment using
methylene chloride. After the extracted organic phase was washed with
water, the organic phase was obtained by separation. After the organic
phase was dried using magnesium sulfate, the organic phase was condensed
at a reduced pressure. The residual material was refined using a silica
gel chromatography (solvent: dichloromethane/cyclohexane=1/1). Thus, 2.15
g of a white amorphous material (i.e., the target compound) was obtained.
The IR spectrum of the compound is illustrated in FIG. 9.

[0112]As mentioned above, the vinyl compounds having formula (1) for use
in the photoreceptor of the present invention can be easily prepared by
using a combination of an aldehyde compound and a phosphonium salt
compound or a combination of a bromo compound and a boronic acid compound
as intermediates. The other compounds listed in Table 1 can also be
prepared by a similar method.

[0113]Vinyl group-containing triarylamine compounds having formula (1) are
used for imparting good charge transportability to the resultant
crosslinked material (layer). The content of the unit obtained from a
vinyl group-containing triarylamine compound in the crosslinking layer is
preferably from 20 to 80% by weight, and more preferably from 30 to 70%
by weight. When the content of the unit in the crosslinked layer is too
low, the charge transportability of the resultant layer deteriorates,
resulting in deterioration of the electric properties of the
photoreceptor (such as deterioration photosensitivity of the
photoreceptor and increase of potential of irradiated portions (i.e.,
residual potential) of the photoreceptor) after repeated use. In
contrast, when the content is too high, the crosslinking density of the
resultant layer decreases because the content of the unit obtained from a
radically polymerizable monomer decreases, and thereby the desired
property (excellent abrasion resistance) cannot be acquired.

[0114]Next, the method for forming a layer including the above-mentioned
crosslinked material will be explained.

[0115]The layer can be typically prepared by coating a coating liquid
including a radically polymerizable tri- or more-functional monomer and a
vinyl group-containing triarylamine compound having formula (1), and
optionally including a radically polymerizable polycarbonate, and then
drying the coated liquid to polymerize the compounds.

[0116]When the polymerizable monomer used is liquid, other components to
be included in the coating liquid may be dissolved therein. In this case,
the coating liquid can be prepared without using a solvent. However, if
necessary, solvents can be used for preparing the coating liquid.

[0117]Specific examples of the solvents include alcohols such as methanol,
ethanol, propanol, and butanol; ketones such as acetone, methyl ethyl
ketone, methyl isobutyl ketone, and cyclohexanone; esters such as ethyl
acetate, and butyl acetate; ethers such as tetrahydrofuran, dioxane, and
propyl ether; halogenated solvents such as dichloromethane,
dichloroethane, trichloroethane, and chlorobenzene; aromatic solvents
such as benzene, toluene, and xylene; cellosolves such as methyl
cellosolve, ethyl cellosolve and cellosolve acetate; etc. These solvents
can be used alone or in combination. The added amount of a solvent is not
particularly limited, and is determined depending on the solubility of
the components, coating methods, and the target thickness of the
protective layer. Suitable coating methods for use in coating the coating
liquid include dip coating, spray coating, bead coating, and ring
coating.

[0118]In order to relax the stress of the crosslinked layer and to improve
the adhesion of the layer to the adjacent layer, the coating liquid can
include additives such as plasticizers, leveling agent, and low molecular
weight charge transport materials having no radical polymerizability.

[0119]Specific examples of the plasticizers include known plasticizers for
use in general resins, such as dibutyl phthalate, and dioctyl phthalate.
The added amount of the plasticizers in the coating liquid is preferably
not greater than 20% by weight, and more preferably not greater than 10%
by weight, based on the total of solid components included in the coating
liquid.

[0120]Specific examples of the leveling agents include silicone oils (such
as dimethylsilicone oils, and methylphenylsilicone oils), and polymers
and oligomers having a perfluoroalkyl group in their side chains. The
added amount of the leveling agents is preferably not greater than 3% by
weight based on the total of solid components included in the coating
liquid.

[0121]After the coating liquid is coated, the coated liquid is subjected
to a heat drying treatment. In this heat drying treatment, the layer is
crosslinked. In order to attain the object of the present invention, the
crosslinked material preferably has a gel fraction of not less than 95%,
and more preferably not less than 97%. In this regard, the gel fraction
of a crosslinked material is determined by the following method. (1) At
first, a crosslinked material, which has been weighed (the weight is W1),
is dipped in an organic solvent having high dissolving power (such as
tetrahydrofuran) for 5 days; and (2) after drying the solvent, the
crosslinked material is weighed (the weight is W2) again to determine the
weight loss. The gel fraction can be determined by the following
equation.

GF (%)=100×(W2/W1),

wherein GF represents the gel fraction of the crosslinked material; W1
represents the weight of the crosslinked material before the dipping
treatment; and W2 represents the weight of the crosslinked material after
the dipping treatment.

[0122]In order to prepare a crosslinked layer having a gel fraction of not
less than 95% (and preferably not less than 97%), the coated layer is
preferably dried at a temperature not lower than 130° C. and more
preferably not lower than 150° C. When the crosslinked layer has
such a high gel fraction, occurrence of the sticking problem in that
inorganic fillers such as silica stick into the layer can be prevented.

[0123]The layer structure of the photoreceptor of the present invention is
not particularly limited, but the crosslinked layer is preferably the
outermost layer of the photoreceptor. Since the compound having formula
(1) has good hole transportability, the crosslinked layer is preferably
formed as the outermost layer of photoreceptors used for negative
charging methods.

[0124]The photoreceptor of the present invention specifically includes a
substrate, an undercoat layer located on the substrate, a charge
generation layer located on the undercoat layer, a charge transport layer
located on the charge generation layer and including the crosslinked
material. In this case, the charge transport layer cannot be well
crosslinked depending on the crosslinking conditions when the charge
transport layer is relatively thick. Therefore, it is preferable to form
a crosslinked second charge transport layer, which includes the
crosslinked material, on the (first) charge transport layer.

[0125]The crosslinked second charge transport layer preferably has a
thickness of not less than 3 μm. When the thickness is less than 3
μm, the charge transport components included in the first charge
transport layer migrate into the second charge transport layer in the
second charge transport layer coating process, thereby affecting the
crosslinking reaction, resulting in decrease of the crosslinking density
of the second charge transport layer. Thus, by forming a crosslinked
second charge transport layer having a thickness of not less than 3
μm, the resultant layer has a high crosslinking density, and thereby
occurrence of the sticking problem can be prevented. In addition, when
the outermost layer is abraded after long repeated use in such a manner
that the ratio of the thickness of the abraded portion of the layer to
the original thickness of the layer is relatively large, the charging
properties and photosensitivity of the photoreceptor seriously change.
From this point of view, the crosslinked second charge transport layer
preferably has a thickness of not less than 3 μm.

[0126]Thus, the photoreceptor of the present invention preferably includes
a substrate, and a charge generation layer, a (first) charge transport
layer, and a crosslinked (second) charge transport layer including the
crosslinked material, which layers are overlaid on the substrate in this
order. The photoreceptor optionally includes other layers such as an
undercoat layer located between the substrate and the charge generation
layer.

[0127]Next, the layers will be explained in detail.

(Charge Generation Layer)

[0128]The charge generation layer includes a charge generation material
having a charge generation function as a main component, and optionally
includes a binder resin and other components.

[0129]Known charge generation materials such as inorganic charge
generation materials and organic charge generation materials can be used
as the charge generation material. Specific examples of the inorganic
charge generation materials include crystalline selenium, amorphous
selenium, selenium-tellurium compounds, selenium-tellurium-halogen
compounds, selenium-arsenic compound, amorphous silicon, etc. In
addition, amorphous silicon in which a dangling bond is terminated with a
hydrogen atom or a halogen atom or in which a boron atom, a phosphorous,
atom is doped can be preferably used.

[0131]Specific examples of the binder resins, which are optionally
included in the charge generation layer, include polyamide, polyurethane,
epoxy resins, polyketone, polycarbonate, silicone resins, acrylic resins,
polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene,
poly-N-vinylcarbazole, polyacrylamide, etc. These resins can be used
alone or in combination.

[0132]In addition, charge transport polymers having a charge transport
function such as (1) polymers (e.g., polycarbonates, polyesters,
polyurethanes, polyethers, polysiloxanes, and acrylic resins), which have
an arylamine skeleton, a benzidine skeleton, a hydrazone skeleton, a
carbazole skeleton, a stilbene skeleton, and/or a pyrazoline skeleton,
and (2) polymers having a polysilane skeleton can also be used alone or
in combination as the binder resin.

[0138]The method for preparing the charge generation layer is not
particularly limited, and a proper method is selected. For example,
vacuum thin film forming methods, and casting methods using a
solution/dispersion can be used.

[0139]Specific examples of such vacuum thin film forming methods include
vacuum evaporation methods, glow discharge decomposition methods, ion
plating methods, sputtering methods, reaction sputtering methods, CVD
(chemical vapor deposition) methods, and the like methods. A layer of the
above-mentioned inorganic and organic materials can be formed by one of
these methods.

[0140]The casting methods useful for forming the charge generation layer
include, for example, the steps of preparing a coating liquid by
dispersing an inorganic or organic charge generation material in a
solvent optionally together with a binder resin using a dispersing
machine such as ball mills, attritors, sand mills, and bead mills; and
coating the dispersion after diluting the dispersion, if necessary, to
prepare the charge generation layer.

[0142]The charge generation layer coating liquid can include a leveling
agent such as dimethylsilicone oils and methylphenyl silicone oils.

[0143]The thickness of the charge generation layer is preferably from 0.01
to 5 μm, and more preferably from 0.05 to 2 μm.

(Charge Transport Layer)

[0144]The charge transport layer has a function of retaining the charges
supplied by a charger, and another function of transporting the charges
generated in the charge generation layer to the surface thereof to couple
the charges with the retained charges on the surface thereof, resulting
in formation of an electrostatic latent image on the charge transport
layer. In order to retain charges, the charge transport layer preferably
has a high electric resistance. In order to obtain a high surface
potential, the layer preferably has a low dielectric constant. Further,
in order to efficiently transport charges, the layer preferably has a
high charge mobility.

[0145]The charge transport layer includes at least a charge transport
material, and optionally includes a binder resin and other components.

[0146]The positive hole transport materials, electron transport materials,
and charge transport polymers mentioned above for use in the charge
generation layer can be used as the charge transport material.

[0147]Specific examples of the charge transport polymers include the
following.

(a) Polymers having a carbazole ring such as polyvinyl carbazole, and
compounds listed in JP-As 50-82056, 54-9632, 54-11737, 04-175337,
04-183719 and 06-234841.(b) Polymers having a hydrozone structure such as
compounds listed in JP-As 57-78402, 61-20953, 61-296358, 01-134456,
01-179164, 03-180851, 03-180852, 03-50555, 05-310904 and 06-234840.(c)
Polysilylene compounds such as compounds listed in JP-As 63-285552,
01-88461, 04-264130, 04-264131, 04-264132, 04-264133 and 04-289867.(d)
Polymers having a triarylamine structure such as
N,N-bis(4-methylphenyl)-4-aminopolystyrene, and compounds listed in JP-As
01-134457, 02-282264, 02-304456, 04-133065, 04-133066, 05-40350 and
05-202135.(e) Other polymers such as nitropyrene-formaldehyde
condensation polymers and compounds listed in JP-As 51-73888, 56-150749,
06-234836 and 06-234837.

[0149]Further, the polymers having an electron donating group are not
limited to the above-mentioned polymers, and copolymers (such as block
copolymers, graft copolymers, star polymers) of the above-mentioned
polymers with known monomers, and crosslinked polymers having an electron
donating group and disclosed in JP-A 03-109406 can also be used.

[0151]The charge transport layer can include a copolymer obtained from a
crosslinkable binder resin and a crosslinkable charge transport material.

[0152]The charge transport layer can be typically prepared by coating a
coating liquid, which is prepared by dissolving or dispersing a charge
transport material and a binder resin in a proper solvent, on the charge
generation layer mentioned above, followed by drying.

[0153]The solvents mentioned above for use in preparing the charge
generation layer can be used for the charge transport layer coating
liquid. Among the solvents, solvents which can well dissolve the charge
transport material and binder resin used can be preferably used. The
solvents can be used alone or in combination.

[0156]Specific examples of the plasticizers include plasticizers for use
in general resins such as dibutyl phthalate and dioctyl phthalate. The
added amount of a plasticizer is 0 to 30 parts by weight per 100 parts by
weight of the binder resin included in the charge transport layer coating
liquid.

[0157]Specific examples of the leveling agents include silicone oils such
as dimethyl silicone oils and methyl phenyl silicone oils; and polymers
and oligomers having a side chain including a perfluoroalkyl group. The
added amount of a leveling agent is 0 to 1 parts by weight per 100 parts
by weight of the binder resin included in the charge transport layer
coating liquid.

[0158]The thickness of the charge transport layer is not particularly
limited, and is determined depending on the applications of the
photoreceptor. In general, the thickness of the charge transport layer is
from 5 to 40 μm, and preferably from 10 to 30 μm.

(Substrate)

[0159]Next, the substrate of the photoreceptor will be explained. Suitable
materials for use as the substrate include materials having a volume
resistivity not greater than 1010Ωcm. Specific examples of
such materials include plastic cylinders, plastic films or paper sheets,
on the surface of which a layer of a metal such as aluminum, nickel,
chromium, nichrome, copper, gold, silver, and platinum, or a metal oxide
such as tin oxides, and indium oxides, is formed using a deposition or
sputtering method. In addition, a plate of a metal such as aluminum,
aluminum alloys, nickel and stainless steel can be used as the substrate.
A metal cylinder can also be used as the substrate. Such a metal cylinder
is prepared by tubing a metal such as aluminum, aluminum alloys, nickel
and stainless steel by a method such as impact ironing or direct ironing,
and then subjecting the surface of the tube to cutting, super finishing,
polishing and the like treatments. Further, endless belts of a metal such
as nickel, and stainless steel, which are disclosed, for example, in JP-A
52-36016, can also be used as the substrate.

[0161]Such an electroconductive layer can be formed by coating a coating
liquid in which an electroconductive powder and a binder resin are
dispersed or dissolved in a proper solvent such as tetrahydrofuran,
dichloromethane, methyl ethyl ketone, toluene and the like solvent, and
then drying the coated liquid.

[0162]In addition, substrates, in which an electroconductive resin film is
formed on a surface of a cylindrical substrate using a heat-shrinkable
resin tube which is made of a combination of a resin such as polyvinyl
chloride, polypropylene, polyesters, polyvinylidene chloride,
polyethylene, chlorinated rubber and fluorine-containing resins (such as
polytetrafluoro ethylene), with an electroconductive material, can also
be used as the substrate.

(Intermediate Layer)

[0163]An intermediate layer can be formed between the charge transport
layer and the crosslinked charge transport layer to prevent migration of
a material (such as charge transport materials), which is included in the
charge transport layer, into the crosslinked charge transport layer or to
improve the adhesion between the two layers. Therefore, it is preferable
that the intermediate layer is insoluble or hardly soluble in the
crosslinked charge transport layer coating liquid. The intermediate layer
includes a binder resin as a main component, which is preferably
insoluble or hardly soluble in the crosslinked charge transport layer
coating liquid. Specific examples of the binder resin include polyamide,
alcohol-soluble polyamide (alcohol-soluble nylon), water-soluble
polyvinyl butyral, polyvinyl alcohol, etc. Suitable methods for preparing
the intermediate layer include the coating methods mentioned above for
use in preparing the charge generation layer and charge transport layer.

[0164]The thickness of the intermediate layer is not particularly limited,
and is determined depending on the applications of the photoreceptor. The
thickness of the intermediate layer is preferably from 0.05 to 2 μm.

(Undercoat Layer)

[0165]The photoreceptor of the present invention can have an undercoat
layer between the substrate and the photosensitive layer (charge
generation layer). The undercoat layer includes a resin as a main
component. Since the upper layer (such as the photosensitive layer or
charge generation layer) is formed on the undercoat layer typically by
coating a liquid including an organic solvent, the resin included in the
undercoat layer preferably has good resistance to general organic
solvents.

[0167]The undercoat layer can include a metal oxide powder to prevent
formation of moire in the resultant images and to decrease residual
potential of the resultant photoreceptor. Specific examples of such metal
oxides include titanium oxide, silica, alumina, zirconium oxide, tin
oxide, indium oxide, etc.

[0168]The undercoat layer can be formed by coating a coating liquid using
a proper solvent and a proper coating method.

[0169]The undercoat layer may be formed using a silane coupling agent,
titanium coupling agent or a chromium coupling agent. In addition, a
layer of aluminum oxide which is formed by an anodic oxidation method,
and a layer of an organic compound such as polyparaxylylene or an
inorganic compound such as SiO, SnO2, TiO2, ITO or CeO2
which is formed by a vacuum evaporation method can also be preferably
used as the undercoat layer. The thickness of the undercoat layer is
preferably 0 to 5 μm.

[0170]In order to impart high stability to withstand environmental
conditions to the resultant photoreceptor (particularly, to prevent
deterioration of photosensitivity and increase of residual potential), an
antioxidant can be included in each of the above-mentioned layers (i.e.,
the crosslinked charge transport layer, charge transport layer, charge
generation layer, undercoat layer, and intermediate layer).

[0171]Suitable materials for use as the antioxidant include phenolic
compounds, paraphenylene diamine compounds, hydroquinone compounds,
sulfur-containing organic compounds, phosphorus-containing organic
compounds, etc. These compounds can be used alone or in combination.

[0178]These compounds are commercialized as antioxidants for rubbers,
plastics, oil and fats.

[0179]The added amount of an antioxidant in a layer is not particularly
limited, and is preferably from 0.01 to 10% by weight based on the weight
of the layer to which the antioxidant is added.

[0180]Next, the image forming method and apparatus of the present
invention will be explained by reference to drawings.

[0181]FIG. 1 is a schematic view illustrating the image forming section of
an embodiment of the image forming apparatus of the present invention.
The image forming apparatus includes a photoreceptor 1 which is the
above-mentioned photoreceptor of the present invention. The image forming
method and apparatus of the present invention perform at least a charging
process in which the photoreceptor 1 is charged with a charger 3; alight
irradiating process in which a light irradiating device 5 irradiates the
charged photoreceptor 1 with imagewise light to form an electrostatic
image thereon; a developing process in which a developing device 6
develops the electrostatic image with a developer including a toner to
form a toner image on the photoreceptor 1; a transfer process in which a
transferring device (including a transfer charger 10 and a separation
charger 11) transfers the toner image to a receiving material 9; a fixing
process in which a fixing device (not shown) fixes the toner image to the
receiving material 9; and a cleaning process in which a cleaner
(including a fur brush 14 and a blade 15) cleans the surface of the
photoreceptor after the transfer process. The photoreceptor 1 is
optionally subjected to a discharging process, in which charges remaining
on the photoreceptor 1 are discharged using a discharger 2, after the
transfer process. Numerals 4 and 7 respectively denote an eraser
configured to erase a part of the charged portion of the photoreceptor 1,
and a pre-transfer charger configured to previously charge the
photoreceptor 1 so that the toner image can be well transferred onto the
receiving material 9. Numerals 8 and 12 respectively denote a pair of
registration rollers configured to timely feed the receiving material 9
to the transferring device 10/11, and a separation pick configured to
separate the receiving material 9 from the photoreceptor 1. Numeral 13
denotes a pre-cleaning charger configured to previously charge the
photoreceptor 1 so that the surface of the photoreceptor can be well
cleaned with the cleaner.

[0182]The photoreceptor 1 has a drum form, but sheet-form or
endless-belt-form photoreceptors can also be used for the image forming
apparatus of the present invention.

[0183]Suitable chargers for use in the charger 3, pre-transfer charger 7,
transfer charger 10, separation charger 11, and pre-cleaning charger 13
include known chargers capable of uniformly charging the photoreceptor,
such as corotrons, scorotrons, solid state dischargers, charging rollers,
etc. Combinations of a transfer charger and a separation charger are
preferably used for the transfer device.

[0184]Suitable light sources for use in the light irradiating device
include fluorescent lamps, tungsten lamps, halogen lamps, mercury lamps,
sodium lamps, light emitting diodes (LEDs), laser diodes (LDs), light
sources using electroluminescence (EL), and the like. In addition, in
order to obtain light having a desired wave length range, filters such as
sharp-cut filters, band pass filters, near-infrared cutting filters,
dichroic filters, interference filters, color temperature converting
filters and the like can be used. Such light sources can also be used for
a transfer process, a discharging process, a cleaning process, and a
pre-exposure process, which use light irradiation. It is preferable that
the light irradiating device 5 performs digital optical recording, i.e.,
the device preferably irradiates the photoreceptor with light modulated
by digital image signals.

[0185]The developing device 6 develops the electrostatic latent image
formed on the photoreceptor 1 with a developer including a toner.
Suitable developing methods include dry developing methods (such as one
component developing methods using a toner as the developer and two
component developing methods using a developer including a carrier and a
toner).

[0186]When the photoreceptor 1, which is previously charged positively (or
negatively), is exposed to imagewise light, an electrostatic latent image
having a positive (or negative) charge is formed on the photoreceptor 1.
When the latent image having a positive (or negative) charge is developed
with a toner having a negative (or positive) charge, a positive image can
be obtained. In contrast, when the latent image having a positive
(negative) charge is developed with a toner having a positive (negative)
charge, a negative image (i.e., a reversal image) can be obtained.

[0187]Known developing devices can be used for the developing process.

[0188]When the toner image thus formed on the photoreceptor 1 by the
developing device 6 is transferred onto the receiving material 9, the
entire toner image is not necessarily transferred onto the receiving
material 9, and toner particles remain on the surface of the
photoreceptor 1. The residual toner is removed from the photoreceptor 1
by the fur brush 14 and cleaning blade 15. In order to well clean the
surface of the photoreceptor 1, the pre-cleaning charger 13 can be used.
Other cleaning methods using only a brush (such as fur brushes and
mag-fur brushes can also be used.

[0189]After the cleaning process, the residual charges on the
photoreceptor are removed by the discharger 2. Known discharging devices
can be used as the discharger 2.

[0190]FIG. 2 illustrates another embodiment of the image forming apparatus
of the present invention. Numeral 21 designates a photoreceptor which is
the photoreceptor of the present invention mentioned above.

[0191]Referring to FIG. 2, the photoreceptor 21 has a belt-form. The
photoreceptor 21 is rotated by rollers 22a and 22b. The photoreceptor 21
is charged with a charger 23, and then exposed to imagewise light emitted
by a light irradiating device 24 to form an electrostatic latent image on
the photoreceptor 21. The latent image is developed with a developing
device (not shown) to form a toner image on the photoreceptor 21. The
toner image is transferred onto a receiving paper (not shown) using a
transfer charger 25. After the toner image transferring process, the
surface of the photoreceptor 21 is cleaned with a cleaning brush 27 after
performing a pre-cleaning light irradiating operation using a
pre-cleaning light irradiator 26. Next, the photoreceptor 21 is
discharged by being exposed to light emitted by a discharging light
source 28. In the pre-cleaning light irradiating process, light
irradiates the photoreceptor 21 from the substrate side of the
photoreceptor 21. In this case, the substrate of the photoreceptor 21 has
to be light-transmissive.

[0192]The image forming apparatus of the present invention is not limited
to the image forming apparatus as shown in FIGS. 1 and 2. For example, in
FIG. 2, the pre-cleaning light irradiating operation can be performed
from the photosensitive layer side of the photoreceptor 21. In addition,
the light irradiation in the light image irradiating process and the
discharging process may be performed from the substrate side of the
photoreceptor 21.

[0193]Further, a pre-transfer light irradiation operation, which is
performed before the transferring of the toner image, and a preliminary
light irradiation operation, which is performed before the imagewise
light irradiation, and other light irradiation operations may also be
performed.

[0194]The above-mentioned image forming unit can be fixedly set in an
image forming apparatus such as copiers, facsimiles and printers.
However, the image forming unit may be set in the image forming apparatus
as a process cartridge. The process cartridge of the present invention
means an image forming unit which includes a photoreceptor, which is the
photoreceptor of the present invention, and at least one of a charger, an
imagewise light irradiating device, a developing device, a transferring
device and a cleaner. The process cartridge is detachably attachable to
the image forming apparatus, for example, using a guide rail.

[0195]FIG. 3 is a schematic view illustrating an embodiment of the process
cartridge of the present invention. In FIG. 3, the process cartridge
includes a photoreceptor 16 which is the photoreceptor of the present
invention, a charger 17 configured to charge the photoreceptor 16, a
developing device (a developing roller) 20 configured to develop a latent
image on the photoreceptor with a toner, an image transfer device 56
configured to transfer the toner image onto a receiving paper, and a
cleaning device 18 (brush) configured to clean the surface of the
photoreceptor 16. After the charging process, the charged photoreceptor
is exposed to imagewise light 19 emitted by a light irradiating device to
form an electrostatic latent image on the photoreceptor 16.

[0196]The image forming method and apparatus, and the process cartridge of
the present invention use the photoreceptor of the present invention
including, as an outermost layer, a crosslinked charge transport layer
which has excellent abrasion resistance and scratch resistance without
causing cracking and peeling problems. Therefore, the image forming
method and apparatus, and process cartridge can be preferably used for
electrophotographic image forming apparatuses such as copiers, laser
printers, CRT printers, LED printers, liquid crystal printers, and laser
plate making machines.

[0197]Having generally described this invention, further understanding can
be obtained by reference to certain specific examples which are provided
herein for the purpose of illustration only and are not intended to be
limiting. In the descriptions in the following examples, the numbers
represent weight ratios in parts, unless otherwise specified.

EXAMPLES

[0198]At first, examples of the photoreceptor having a layer including a
crosslinked material obtained by polymerizing a vinyl group-containing
triarylamine compound having formula (1) and a radically polymerizable
tri- or more-functional monomer having no charge transport structure will
be explained.

Example 1

Formation of Undercoat Layer

[0199]The following components were mixed to prepare an undercoat layer
coating liquid.

[0200]The undercoat layer coating liquid was applied on a surface of an
aluminum drum having an outside diameter of 30 mm, and the coated liquid
was dried. Thus, an undercoat layer having a thickness of 3.5 μm was
prepared.

(Formation of Charge Generation Layer)

[0201]The following components were mixed to prepare a charge generation
layer coating liquid.

[0204]The charge transport layer coating liquid was applied on the charge
generation layer, and the coated liquid was heated to be dried, resulting
in preparation of a charge transport layer having a thickness of 18
μm.

[0206]The coating liquid was applied on the charge transport layer using a
spray coating method, and the coated liquid was dried for 30 minutes at
130° C. Thus, a crosslinked charge transport layer having a
thickness of 5.0 μm was prepared.

[0207]Thus, a photoreceptor of Example 1 was prepared.

Example 2

[0208]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the compound No. 1 used for the crosslinkable charge
transport layer coating liquid was replaced with the compound No. 3
listed in Table 1.

[0209]Thus, a photoreceptor of Example 2 was prepared.

Example 3

[0210]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the compound No. 1 used for the crosslinkable charge
transport layer coating liquid was replaced with the compound No. 5
listed in Table 1.

[0211]Thus, a photoreceptor of Example 3 was prepared.

Example 4

[0212]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the temperature at which the coated crosslinkable
charge transport layer coating liquid was dried was changed from 130 to
140° C.

[0213]Thus, a photoreceptor of Example 4 was prepared.

Example 5

[0214]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the temperature at which the coated crosslinkable
charge transport layer coating liquid was dried was changed from
130° C. to 150° C.

[0215]Thus, a photoreceptor of Example 5 was prepared.

Example 6

[0216]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the temperature at which the coated crosslinkable
charge transport layer coating liquid was dried was changed from
130° C. to 150° C. and the compound No. 1 used for the
crosslinkable charge transport layer coating liquid was replaced with the
compound No. 3.

[0217]Thus, a photoreceptor of Example 6 was prepared.

Example 7

[0218]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 1.0 μm.

[0219]Thus, a photoreceptor of Example 7 was prepared.

Example 8

[0220]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 3.0 μm.

[0221]Thus, a photoreceptor of Example 8 was prepared.

Example 9

[0222]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 7.0 μm.

[0223]Thus, a photoreceptor of Example 9 was prepared.

Example 10

[0224]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 Tim to 10.0 μm.

[0225]Thus, a photoreceptor of Example 10 was prepared.

Example 11

[0226]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 12.0 μm.

[0227]Thus, a photoreceptor of Example 11 was prepared.

Comparative Example 1

[0228]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the compound No. 1 was replaced with a comparative
compound No. 1 having formula (1) in which the group Ar has the following
formula.

##STR00024##

[0229]Thus, a photoreceptor of Comparative Example 1 was prepared.

Comparative Example 2

[0230]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the compound No. 1 was replaced with a comparative
compound No. 2 having formula (1) in which the group Ar has the following
formula.

##STR00025##

[0231]Thus, a photoreceptor of Comparative Example 2 was prepared.

Comparative Example 3

[0232]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the compound No. 1 was replaced with a comparative
compound No. 3 having the following formula.

##STR00026##

[0233]Thus, a photoreceptor of Comparative Example 3 was prepared.

Comparative Example 4

[0234]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the compound No. 1 was replaced with a comparative
compound No. 4 having the following formula.

##STR00027##

[0235]Thus, a photoreceptor of Comparative Example 4 was prepared.

Example 12

[0236]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the crosslinkable charge transport layer coating
liquid was replaced with the following crosslinkable charge transport
layer coating liquid.

[0237]Trimethylolpropane triacrylate 10 parts

[0238](KAYARAD TMPTA from Nippon Kayaku Co., Ltd., having molecular weight
(M) of 296, number of functional groups (N) of 3, and ratio (M/N) of 99)

[0240]The procedure for preparation of the photoreceptor in Example 12 was
repeated except that the compound No. 1 in the crosslinkable charge
transport layer coating liquid was replaced with the compound No. 3
listed in Table 1.

[0241]Thus, a photoreceptor of Example 13 was prepared.

Comparative Example 5

[0242]The procedure for preparation of the photoreceptor in Example 12 was
repeated except that the compound No. 1 was replaced with the comparative
compound No. 2 used in Comparative Example 2.

[0243]Thus, a photoreceptor of Comparative Example 5 was prepared.

Comparative Example 6

[0244]The procedure for preparation of the photoreceptor in Example 12 was
repeated except that the compound No. 1 was replaced with the comparative
compound No. 3 used in Comparative Example 3.

[0245]Thus, a photoreceptor of Comparative Example 6 was prepared.

Example 14

[0246]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the crosslinkable charge transport layer coating
liquid was replaced with the following crosslinkable charge transport
layer coating liquid.

[0248]The procedure for preparation of the photoreceptor in Example 14 was
repeated except that the compound. No. 1 in the crosslinkable charge
transport layer coating liquid was replaced with the compound No. 3
listed in Table 1.

[0249]Thus, a photoreceptor of Example 15 was prepared.

Comparative Example 7

[0250]The procedure for preparation of the photoreceptor in Example 14 was
repeated except that the compound No. 1 was replaced with the comparative
compound No. 2 used in Comparative Example 2.

[0251]Thus, a photoreceptor of Comparative Example 7 was prepared.

Comparative Example 8

[0252]The procedure for preparation of the photoreceptor in Example 14 was
repeated except that the compound No. 1 was replaced with the comparative
compound No. 4 used in Comparative Example 4.

[0253]Thus, a photoreceptor of Comparative Example 8 was prepared.

[0254]Next, examples of the photoreceptor having a layer including a
crosslinked material obtained by polymerizing a vinyl group-containing
triarylamine compound having formula (1), a radically polymerizable
polycarbonate, and a radically polymerizable tri- or more-functional
monomer having no charge transport structure will be explained.

Example 16

[0255]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the crosslinkable charge transport layer coating
liquid was replaced with the following crosslinkable charge transport
layer coating liquid.

[0257]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the compound No. 1 was replaced with the compound
No. 3 listed in Table 1.

[0258]Thus, a photoreceptor of Example 17 was prepared.

Example 18

[0259]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the compound No. 1 was replaced with the compound
No. 5 listed in Table 1.

[0260]Thus, a photoreceptor of Example 18 was prepared.

Example 19

[0261]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the temperature at which the coated crosslinkable
charge transport layer coating liquid was dried was changed from
130° C. to 140° C.

[0262]Thus, a photoreceptor of Example 19 was prepared.

Example 20

[0263]The procedure for preparation of the photoreceptor in Example 1 was
repeated except that the temperature at which the coated crosslinkable
charge transport layer coating liquid was dried was changed from
130° C. to 150° C.

[0264]Thus, a photoreceptor of Example 20 was prepared.

Example 21

[0265]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the temperature at which the coated crosslinkable
charge transport layer coating liquid was dried was changed from
130° C. to 150° C. and the compound No. 1 used for the
crosslinkable charge transport layer coating liquid was replaced with the
compound No. 3.

[0266]Thus, a photoreceptor of Example 21 was prepared.

Example 22

[0267]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 1.0 μm.

[0268]Thus, a photoreceptor of Example 22 was prepared.

Example 23

[0269]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 3.0 μm.

[0270]Thus, a photoreceptor of Example 23 was prepared.

Example 24

[0271]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 7.0 μm.

[0272]Thus, a photoreceptor of Example 24 was prepared.

Example 25

[0273]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 10.0 μm.

[0274]Thus, a photoreceptor of Example 25 was prepared.

Example 26

[0275]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the thickness of the crosslinked charge transport
layer was changed from 5.0 μm to 12.0 μm.

[0276]Thus, a photoreceptor of Example 26 was prepared.

Comparative Example 9

[0277]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the compound No. 1 used for crosslinkable charge
transport layer coating liquid was replaced with the comparative compound
No. 1 used in Comparative Example 1.

[0278]Thus, a photoreceptor of Comparative Example 9 was prepared.

Comparative Example 10

[0279]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the compound No. 1 used for crosslinkable charge
transport layer coating liquid was replaced with the comparative compound
No. 2 used in Comparative Example 2.

[0280]Thus, a photoreceptor of Comparative Example 10 was prepared.

Comparative Example 11

[0281]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that the compound No. 1 used for crosslinkable charge
transport layer coating liquid was replaced with the comparative compound
No. 3 used in Comparative Example 3.

[0282]Thus, a photoreceptor of Comparative Example 11 was prepared.

Example 27

[0283]The procedure for preparation of the photoreceptor in Example 16 was
repeated except that 1,2,4-trivinyl cyclohexane used for the
crosslinkable charge transport layer coating liquid was replaced with 5
parts of trimethylolpropane triacrylate (KAYARAD TMPTA from Nippon Kayaku
Co., Ltd.).

[0284]Thus, a photoreceptor of Example 27 was prepared.

Example 28

[0285]The procedure for preparation of the photoreceptor in Example 27 was
repeated except that the compound No. 1 used for the crosslinkable charge
transport layer coating liquid was replaced with the compound No. 3
listed in Table 1.

[0286]Thus, a photoreceptor of Example 28 was prepared.

Comparative Example 12

[0287]The procedure for preparation of the photoreceptor in Example 27 was
repeated except that the compound No. 1 used for the crosslinkable charge
transport layer coating liquid was replaced with the comparative compound
No. 2 used in Comparative Example 2.

[0288]Thus, a photoreceptor of Comparative Example 12 was prepared.

Comparative Example 13

[0289]The procedure for preparation of the photoreceptor in Example 27 was
repeated except that the compound No. 1 used for the crosslinkable charge
transport layer coating liquid was replaced with the comparative compound
No. 4 used in Comparative Example 4.

[0290]Thus, a photoreceptor of Comparative Example 13 was prepared.

[0291]The gel fraction of the crosslinked charge transport layers of the
photoreceptors of Examples 1-28 and Comparative Examples 1-13 was
measured. The method of measuring the gel fraction is as follows.

[0292]Each of the crosslinkable charge transport layer coating liquids
used in Examples 1-28 and Comparative Examples 1-13 was coated on an
aluminum plate, followed by drying to prepare crosslinked charge
transport layers. In this regard, the drying conditions are the same as
those mentioned above in Examples 1-28 and Comparative Examples 1-13. The
resultant crosslinked charge transport layers were dipped into
tetrahydrofuran for 5 days at 25° C., followed by drying at room
temperature.

[0293]The gel fraction of a crosslinked charge transport layer can be
determined by the following equation.

GF (%)=100×(W2/W1),

wherein GF represents the gel fraction of the crosslinked charge transport
layer; W1 represents the weight of the crosslinked charge transport layer
before the dipping treatment; and W2 represents the weight of the
crosslinked charge transport layer after the dipping treatment and the
subsequent drying treatment.

[0295]The photoreceptors of Examples 1-28 and Comparative Examples 1-13
were subjected to the following running test.

[0296]Each of the photoreceptors was set in an image forming apparatus
(IMAGIO NEO 270 manufactured by Ricoh Co., Ltd.), in which a laser diode
serving as a light source irradiates the photoreceptor, which has been
charged to have a potential of -900V, with light of 655 nm to form an
electrostatic latent image on the photoreceptor, and the electrostatic
latent image is developed with a developer including a toner, which has a
volume average particle diameter of 9.5 μm and an average circularity
of 0.91 and includes a silica as an external additive. Next, a running
test in which 50,000 copies of an original image are continuously
produced was performed. At the beginning and end of the running test, the
potential of an irradiated portion of the photoreceptor, which portion
receives light of 0.4 μJ/cm2, was measured, and the image was
visually observed to determine the image qualities. In addition, the
abrasion loss of the photoreceptor was determined from the difference in
thickness between the photoreceptor before the running test and the
photoreceptor after the running test. Further, the image at the end of
the running test was visually observed to determine the number of white
spots in a solid image.

[0298]It is clear from Tables 3-1 and 3-2 that the photoreceptors of
Examples 1-28 have good abrasion resistance and produce images with a
small number of white spots over a long period of time. This is because
the surface of the photoreceptors is hardly stuck by the silica included
in the toner. Among the photoreceptors of Examples 1-28, the
photoreceptors having a crosslinked charge transport layer having a gel
fraction of not less than 95% are superior in the white spot quality.
Further, the photoreceptors having a crosslinked charge transport layer
having a gel fraction of not less than 97% have excellent abrasion
resistance and hardly produce white spots. When the thickness of the
crosslinked charge transport layer is not less than 3 μm, the
resultant photoreceptors have excellent abrasion resistance and produce
high quality images free from defects.

[0299]Additional modifications and variations of the present invention are
possible in light of the above teachings. It is therefore to be
understood that within the scope of the appended claims the invention may
be practiced other than as specifically described herein.

[0300]This document claims priority and contains subject matter related to
Japanese Patent Application No. 2008-235992, filed on Sep. 16, 2008, the
entire contents of which are herein incorporated by reference.